1. Field of the Invention
The present invention relates to a composite movement table movable in at least a plane including a Z axis, and in particular, to a composite movement table which achieves a high degree of accuracy of parallelism and positioning when the movement table is moved at high speeds, and which provides a chuck for removably holding an exposed member for mounting on the movement table depending on the size of the exposed member.
2. Description of the Prior Art
In the manufacturing process of a semiconductor integrated circuit, lithography is used to expose a wafer coated with photo resist and to develop a desired circuit pattern thereon. Lithography requires highly accurate positioning, on the order of 0.1 micron, due to the trend toward higher integration of the semiconductor integrated circuit.
To achieve such highly accurate positioning is difficult for prior art movement table apparatus in which a movement table is merely moved by a feed screw. For this reason, it has been proposed to use a table which is moved by a screw serving as the coarse adjustment, with a fine adjustment bed movably supported for minute adjustment provided on the coarse adjustment table. The absolute position of the fine adjustment bed is measured by a laser measuring instrument, and an error in the movement of the coarse adjustment table is corrected by a minute displacement of the fine adjustment bed, thereby achieving precise positioning.
The lithography generally employed is projection photo lithography. Projection photo lithography is a so-called step-and-repeat type operation, in which a small integrated circuit pattern is developed on a wafer in sequential steps. This requires maintaining the parallelism and positioning of the light receiving surface of the wafer with high accuracy. Therefore, it is also necessary to maintain the parallelism and positioning of the upper surface of the table for mounting the wafer thereon with high accuracy.
Prior art composite movement tables are, for example, Japanese Utility Model Laid-Open (Kokai) Publication No. 58-196834 and U.S. Pat. No. 4,561,815.
In Japanese Utility Model laid-Open Publication No. 58196834, a Z axis uppermost type of composite table having a Z axis table at the uppermost stage side, as shown in FIG. 2, and a Z axis lowermost type having the Z axis table at the lowermost stage side are disclosed. Both types employ an oblique feeding system utilizing an oblique surface for moving the table in the Z axis direction. Also, they are structured to achieve movement in the Z axis direction by moving a Z slider horizontally.
However, in the aforementioned prior art Z axis uppermost type of composite tables, since the Z slider is mounted on the upper surface of an XY slider, the weight of the Z slider is imposed on the XY slider, resulting in an increase in the inertial mass of the XY slider during operation, rendering it impossible to increase the operation speed. Further, since the load applied on a supporting section of the XY slider is large, it is necessary to increase the strength of the XY slider. Thus, the XY slider becomes large and heavy, making it impossible to make the movement table small in size and light in weight. Moreover, since the XY slider is structured as a separate member and the supporting sections are independent from each other, it is necessary to make the XY movement plane parallel with the upper surface of the Z slider. Hence, an error in the Z direction is apt to be caused by the operation of the XY slider. Thus, this prior art table cannot be used for lithography and similar operations which require strict parallelism.
On the other hand, in the Z axis lowermost type, since the XY slider is mounted on the Z slider, the operation of the XY slider and the operation of the Z slider can be performed independently from each other. Accordingly, when XYZ sliders are used for lithography, the purpose of the Z slider is for focusing. Since the frequency of operation in the Z direction is not so large, there is an advantage in that, even when the XY slider is mounted on the Z slider, the problem of increased inertia can be largely eliminated. However, since it is necessary to work both the Z slider and the XY slider mounted on the Z slider in a tapered shape, the problem still remains that maintaining strict parallelism as required is difficult.
Furthermore, in both the Z axis uppermost type and the Z axis lowermost type, movement in the Z axis is achieved by moving the Z slider in a horizontal direction. Since the Z slider and the table mounted on the Z slider and movable in the Z direction are in contact with each other, with their surfaces forming oblique surfaces, a problem arises in that the more the precision of the surfaces and the roughness of the surfaces are improved, the larger the sliding frictional resistance becomes. It requires great power to move the Z slider, while at the same time stick-slip is likely to occur. This drawback is more serious, in particular, in the Z axis lowermost type of composite table having the XY slider mounted on the Z slider.
In order to solve these problems, one might consider applying the machine tool adjustment disclosed in U.S. Pat. No. 4,561,815 as the Z direction position adjustment mechanism. In this patent, a head slide is supported through ball bearings by a wedge having its upper surface formed as a horizontal surface. By moving the wedge horizontally by a threaded shaft rotated by a stepping motor fixed to the head slide, the head slide is raised or lowered in the Z direction. However, in such a structure, since the stepping motor is fixed to the head slide, vibrations caused by driving the stepping motor are transmitted directly to the head table (Z table). Hence it is difficult to achieve positioning with an accuracy of the order of a sub-micron, as is required in the case of the lithography.
For this reason, as shown in FIG. 2 of the aforementioned U.S. Pat. No. 4,561,815, one might consider attaching the stepping motor to a machine tool frame. If this is done, since the upper surface of the wedge (oblique slider) is an oblique surface, when the XY movement table placed on such wedge is moved in X and Y directions, the XY table is also displaced in the Z direction following the movement in the X and Y directions. Thus, there is a problem in that the Z direction position deviates subsequent to the movement in the X and Y directions. Moreover, another problem arises in that the ball bearings interposed between the wedge and the head slide are shifted downwardly on the oblique surface during use, and smooth operation of the wedge can not be insured. In this case, although the amount of shift of the ball bearing downwardly caused by the movement of the wedge is slight, such shifts accumulate and the amount of shift will be large over time.
Further, lithography of the projection photo type uses the step-and-repeat technique in which an integrated circuit pattern is developed on a wafer one step at a time. Several hundred positionings may be required for one sheet of wafer. Thus, the total time required for the positionings is large, and in order to improve the efficiency of the exposure process, it is necessary that the positioning be performed in a short time.
A prior art apparatus which satisfies this requirement is proposed by the applicant of this application in Japanese Utility Model Laid-Open (Kokai) Publication No. 58-105604. In this prior art apparatus, a fine adjustment bed is resilient supported on a coarse adjustment table. A viscous fluid fills the volume between a vibration damping section formed in the fine adjustment bed and a receiving surface formed on the coarse adjustment table to provide a damping effect for the vibrations.
However, in the above-referenced prior art apparatus, although there is an advantage in that the vibrations caused in the fine adjustment bed when the coarse adjustment table is moved at high speeds are effectively damped by the high viscosity viscous fluid between the damping surface of the damping section and the receiving surface of the coarse adjustment table thereby enabling positioning at high speeds, since the vibration damping section is immersed in the viscous fluid, when the viscosity of the viscous fluid is increased in order to enhance the damping effect of the vibrations, resistance caused by compression of the viscous fluid by a side wall of the vibration damping section at the time when the fine adjustment bed is moved becomes very large. This is not desirable since the movement of the fine adjustment bed is hindered. Accordingly, in order to insure the smooth movement of the fine adjustment bed, the viscosity of the viscous fluid must be sharply decreased, and if this is done, the damping effect of the vibrations will be decreased. Therefore, there remains an unsolved problem in that both the smooth movement of the fine adjustment bed and the damping effect of the vibrations cannot be achieved simultaneously.
Prior art projection photo lithography is incorporated into the production line of the semiconductor integrated circuit in which a circuit pattern is exposed and developed on a wafer. It is usual that such a lithography device is used exclusively for a wafer of an appropriate size.
In such a device, since the size of a wafer placed on a chuck is constant, the size of a wafer holding section of a loading device for loading the wafer onto the chuck is also constant. It is unusual to use different chucks to expose wafers of different sizes. In such a device, the chuck is, for example, secured on an XY table by fastening it with a bolt.
However, in the aforementioned prior art device, the chuck for mounting a member which is to be exposed, such as a wafer or the like, is secured on the movement table with the bolt. There is no problem when the lithography device is used as an exclusive device with a fixed wafer size for mass production. However, when the device is to be used as a multi-purpose device for trial manufacture and experiments, in order to expose members of various sizes, e.g., 2-6 inches, when an exposed member of a small size is placed on the chuck mounted on the movement table, a loading device matched to the wafer size is naturally used. Thus, if the chuck is not changed for one which matches the wafer size, loading of the wafer by the loading device will be impossible. In prior art lithography devices, since the chuck is secured on the movement table by fastening with a bolt, changing the chuck itself is troublesome. Further, wear powder is apt to be formed by the fixing and removing of the bolt. The fear arises that the parallelism of the exposed member mounting surface of the chuck has deviated.